Boot upper



FIG. 1 is a left side view of a boot upper, showing my new design;

FIG. 2 is a left perspective view thereof;

FIG. 3 is a front view thereof;

FIG. 4 is a rear view thereof; and,

FIG. 5 is a top view thereof.

The broken line showing of environment in FIGS. 1-5 is for illustrativepurposes only and forms no part of the claimed design.

The ornamental design for a boot upper, as shown and described.